Xvi INTRODUCTION 
coloured hyphe, or it may be dark and carbonaceous. Frequently 
it is excluded by the growth of the dise (fig. 8). 
In the more highly developed lecanorine apothecium (fig. 9) 
the thalline tissue containing gonidia develops along with the 
thm pm 
Ve 
Fic. 9.—Vertical section of lecanorine apothecium. 
a, asci; p, paraphyses; e, epithecium ; g, gonidia ; 
h, hypothecium; p.m, proper margin; th.m, 
thalline margin. 
other apothecial tissues. 
(Greatly magnified.) 
This outer protective wall or amphi- 
thecium is generally called the ‘“thalline margin” (th.m) ; it 
closely surrounds and forms an integral part of the apothecium. 
Apothecia vary greatly in size from about 0°25 to 10 mm. or 
more in diameter. 
Perithecium.—When the fruit is a closed body with only a 
Kia. 10.—Vertical section of peri- 
thecia. a, entire; b, dimidiate. 
(Greatly enlarged, diagramatic.) 
narrow opening or ostiole it is called 
a perithecium (fig. 10). Generally 
it is surrounded by a wall and the 
perithecium is then entire (a), or 
the wall is absent or reduced to a 
thin line below the base and it is 
then described as dimidiate (b). 
Perithecia are always small bodies 
and usually they are partly im- 
mersed in the thallus or substratum, 
As a rule lichen-fruits grow 
slowly. Spores may be produced 
almost any time in the year, but 
for a number of species there is a 
double spore-bearing season, in spring and again in autumn, 
The same fruits often persist for several years, new asci being 
